Imagine charging your smartwatch or health tracker without ever plugging it in—or even needing a battery.
A team of scientists at UNIST (Ulsan National Institute of Science and Technology, South Korea) has taken a big step toward making this possible.
They’ve developed a tiny solid-state device that turns body heat into usable electricity, opening the door for battery-free wearables and Internet of Things (IoT) sensors.
The research, led by Professor Sung-Yeon Jang from UNIST’s School of Energy and Chemical Engineering, was published in Energy & Environmental Science.
The team created the world’s first high-performance n-type solid-state thermogalvanic cell powerful enough to run real electronic devices.
Thermogalvanic cells are small energy harvesters that generate electricity from temperature differences.
In this case, the difference comes from the human body’s natural warmth—about 36°C—compared with cooler surrounding air, usually 20–25°C.
While this sounds simple, the challenge is that the temperature gap is quite small, and earlier systems couldn’t generate enough power to run everyday devices.
This new invention solves that problem. The solid-state design avoids liquid leakage risks, which makes it safer and easier to integrate into wearables.
Traditionally, solid-state systems struggled because ions inside the material moved too slowly, limiting power.
The UNIST team solved this by engineering an advanced electrolyte that lets ions move more freely. This, combined with a thermally driven process that boosts ion flow, creates stronger voltage and current than ever before.
To put the results into perspective: by stacking 100 of these cells together—like snapping LEGO blocks—the system can generate about 1.5 volts, the same as a typical AA battery.
When 16 of these modules are connected, they can power devices such as LED lights, digital clocks, or temperature and humidity sensors—all using nothing but body heat.
Another impressive achievement is the device’s efficiency. It boasts a Seebeck coefficient (a measure of how much voltage is created from a temperature difference) of –40.05 millivolts per degree Kelvin, which is up to five times higher than earlier n-type devices. The team also tested its durability, showing it remained stable after 50 charge-discharge cycles.
At the heart of the system is a special polymer called PEDOT:PSS combined with iron-based ions. The material forms a stable structure that allows other ions to move freely, helping the device harvest heat energy more effectively.
Professor Jang described the work as “a new milestone in low-temperature waste heat energy harvesting.”
Looking ahead, this technology could provide a clean, reliable power source for flexible electronics, smart health monitors, and autonomous IoT gadgets—no charging, no batteries, just the warmth of your own body.
